Process of making safety paper by one continuous operation



:50 too much andbecome wet.

Patented Dec. 12, 1933 PROCESS OF MAKING SAFETY PAPER "BY ONE CONTINUOUS.OPERATION Frank S. Wood, Quincy, Mass, assignor to Inkset Safety PaperCo., a corporation of Massachusetts No Drawing. Application November 8,1930 Serial No. 494,443

1 Claim.

My invention belongsto that class of safety papers in which the safetyfeature is imparted by treating ordinarywriting paper with a chemicalcompound and more especially with the I chemical compound for which anapplication for a patent was filed by me, on October 13, 1930, SerialNumber 488,545,.

This compound may be made in any quantity by dissolving one grain oftannic acid in each gallon of water and adding 2 to 5 cubic centimetersof glacial acetic acid; to'this add onetenth of a gallon of decolorizediodine; Ordinary paper treated by my process is transmuted into safetypaper which discolors and sets ink written on its surfaces wheneradicators are usedto remove the ink. If only 2 cubic centimeters ofacetic acid are used the inkset will be thrown out and will not appear;the same thing will happen if 6 cubic centimeters or more of acetic :0acid are used. Between'2 and 5 the different colors require differentamounts to get the best results. Different gradesof paper requirespecial formulas to be worked out between the two extremes specified;but anyone skilled in the art may quickly determine the best formula.

Heretofore, safety paper has required two or more operations ormechanical handlings. The first operation is the manufacture'of thepaper, to formula, in the usual way, leaving 'aproxia0 mately 8% ofmoisture (water) in thepaper. The second operation consists in some formof subsequent re-handling involving chemical treatment of the paper orprinting or both which second operation costs, at least, as much ,as the85 first; and this cost is considerably augmented if it be necessary todry out any part of the water content left in the paper by the firstoperation.

The object of my invention is to eliminate the entire cost of the secondoperation and only 4'0 slightly increase the cost-of the first byadapting it to better achieve the combined purposes of both in onecontinuous operation. a

-Paper has, in itself, anaflinity for moisture called absorption thatvaries-with its temperatuxe, with the amount of moistureapplied to it,and withthe chemical character of the liquid supplying the moisture.When chemicals, for which paper has a strong'aflinity, are brought incontact with it, the natural tendency is to absorb In saturated paper,there is a moisture'content of over .After it has gone through threeroll-pressings in the paper machine, it contains 40% of moisture. Forthe'purposes of my invention, ,allp'aper is '65 wet which contains 9% ormore of moisture,

(Cl. ill-67.95)

and any'degree of this range of wetness destroys the purpose of myprocess. It is, therefore, absolutely necessary to control the amount ofmoisture whichthe paper shall absorb "to a very delicate degree. This isdone by having the paper in the right condition at a certain time, byhaving the right positive chemical for absorption by thenegativepapen'and by having the chemical applied to'the'paper under perfectmechanical and chemical controland regulation. All the essentials ofperfect regulation, repressed affinity and mechanical and chemicalsupply, control and application are comprehended in the phrase,mechanico-chemical absorption. Inher'ently, in 7 order for the purposeof'my process to beaccom-' plished, the paper must. be commercially dryafter'the chemicals have been absorbed. No subsequent drying isessential; therefore there can be no previous wetness and especialy nosaturation; otherwise the" paper would be. spoiled. 76 It is a fact thatmy process is diametrically opposite to saturating, wringing, scraping,and then drying; Such methods all apply a surplus of moisture to thepaper, too much moisture for my purpose, and then remove the surplus byvarious methods of elimination subsequent to the application ofmoisture. .With my process there is no wetting of the paper and nosaturation. The paper is prevented from absorbing more than the amountof moisture to make it commercially dry byfseveral mechanical andchemical balanced adjustments. A description of one of my experimentsmay illustrate and clear up any thing lacking. I have taken a web ofpaper dried out to a 3% moisture content as it came from the papermachine and have run that web, while still warm, through a machinecomprised of a battery of spray-guns. These guns use compressed air atany desired pressure which spray a very fine. fog of chemical upon thesurfaces of 95 the paper, the liquid being sucked into the airblastbefore spraying. After being sprayed the paper was wound on a reel,still warm, and felt dry to the touch. It was found to contain 8% ofmoisture. This showed that it. had absorbed 5% 1 of chemical compound.It was neither saturated nor wet; it was dry and yet it had gone throughno drying subsequent to the. application of chemicals. The reason wasthat the moisture, being controlled and properly applied 105 to the warmand super-dry paper, is absorbed by thepaper without any'perceptiblemoistening of its surface. By no possibility can any coating, saturatingor oiling machine function in this way when using other liquids thanoil. 011 and 110 water work entirely different on paper. In my process,it is a combination of delicate means, conditions and balances, at justthe right time and place that constitutes the novelty of my invention.

In brief, my invention consists of a process involving dehydration andsubsequent mechanicochemical absorption.

To this end, my invention eliminates the necessity of drying out thepaper in a second handling, by dehydrating it as it is being made. Thismay be accomplished in two ways: Either by slowing down the speed of thepaper-making machine and thus increase the time that the paper is on thedrying-rolls, or by adding two steam drying-rolls to the paper-makingmachine which gives the same result. This turns outa paper which isknown to the art as bone-dry.

In this condition, the bone-dry, hot paper is threaded through thecalender-stack for the purpose of giving it the desired finish which, ina writing paper, would'probably be either a bond or a ledger finish.Having received its finish, the hot paper then is permitted to absorbapproximately 8%, by weight, of a chemical com-' pound adapted totransform the paper into safety paper. The chemical compound whichsupplies the moisture for absorption by the paper, may or may not be thechemical compound which has hereinbefore been mentioned as the subjectof separate patent proceedings, as my invention comprehends the use ofany chemical compound which produces safety paper in one continuousoperation through the two steps of dehydration and subsequentmechanico-chemical absorption.

The amount of moisture which any paper may absorb without damage isapproximately 8% of its bone-dry weight; and this is also theapproximate amount of chemical compound necessary to produce acommercial, clear-stock safety paper by my process. While it is possibleto strengthen and adapt a chemical formula to 1% or possibly 2% of watercontent left in the paper before being chemically treated, it is notsafe to go beyond that, for the reason that any moisture ed or putthrough my process.

moisture, whether it be water, chemical comleft in the paper will, by somuch, prevent the absorption of chemical compound, and insufiicientchemical compound may have the same effect upon the paper as if it hadnever been treat- Again, too much pound or both will cause the paper towind-up in a perfect honeycomb of wrinkles; an uneven application ofmoisture will make the paper,

draw, fold and even break, wasting both paper and compound. Hence, thenecessity for a very fine adjustment of moisture in the form of chemicalcompound to be delivered to the paper for absorption. Having absorbedits predetermined,

' regulable and controlled quota of chemical compound, the paperthen-goes to the winder where it is made into a roll, thus completingthe process of producing a safety paper at one continuous operation.

to the fraction of 1%. However, any moisturecontrol device with a finedegree of adjustment will meet the demands of my process. Any attempt toapply the liquid to an upward traveling roll, such as a calender roll,and thence to the paper, results in failure, for two reasons. First,from lack of moisture control; and second, from insufficient treatment.Such application floods the roll with liquid; the speed of the rollcarries the compound upward until it contacts with the paper; but thespeed of the paper together with the nipbetween the calender-rollsnecessary to give the paper the desired finish, blocks absorption by thepaper and results in partial treatment, only. Then again, this method ofapplying moisture is known in the art as a water-finish. Its eifect isto give the paper a gloss. Since a gloss makes a bond finish impossible,only ledger paper may be turned out by such a method.

'Another objection to this method is that the calender-rolls wearunevenly. Where the surface is not true, the'worn part or parts act as atrough through which too much moisture will flow, caus ing the paper topucker, fold and wind up in a damaged condition; while a little more wetwill cause the paper to break, wasting both paper and chemicals. It isto overcome such difiiculties that my process is designed.

Another serious obstacle that has many times defeated the objects andpurposes of their inventors was in having the chemical solution toopowerful or off balance; that is to say, they were too strong, tooalkaline or too acid, any one of which will surely cause the paper todiscolor after being chemically treated. This spoilage and damage endsin complete fiasco. Besides that, heavy damage was caused by ruining thebrass'rolls of the paper-making machine.

With my process, such outcomes are guarded against by using a chemicalcompound so delicately balanced'with effectual acids and bases as to beneutral in all of its contacts. It neither injurespaper machines,equipment, paper nor color. On the contrary, color is preserved by thechemical compound and the fiber of the paper L is improved andstrengthened.

In many paper-mills, it is customary to set the calender-stack close tothe drying-rolls. This makes it impracticable to set up an absorptionunit between the steam-rolls and the calender. If, however, there weresufiicient space between the last drying-roll and the calender toinstall an absorption unit, there is no reason why the chemical compoundcould not be absorbed directly by the bone-dry paper which would, then,be threaded through the calender where it would receive its finish andthen go direct to the winder. Such a set-up would be consistent with thepurposes of my invention and yet it 'might be impracticable to apply inmost existing papermills, on account of lack of space to install the Theresult would be the'same in either I have found that the treatment ofpaper by my process strengthens the fiber so that paper of the sameweight will register a higher bursting strength after going through myprocess than it did before. It is a fact that a pure sulphite paper madefrom wood pulp and put through my process has a higher bursting strengththan an ordinary 60% rag paper.

It is a fact that paper of the most delicate and attractive tints may bemade into a safety paper by my inventions without changing the shade ofthe tint, thus lending itself to the highest demands of thelithographers art in colorful blends, contrasts and pictorialillustrations. This has heretofore been impossible with safety papers.

It is a fact that by giving a sulphite writing paper my process, itsvalue, as represented by the wholesale selling price of inferior safetypapers, will be increased 3 /2 times; while the cost of production willbe increased less than 10%.

What I claim as my invention and desire Letters Patent for is:

Steps in a process of making safety paper by one continuous operationcomprising complete or approximate dehydration and subsequent controlledapplication and absorption of approximately 8% of water, decolorizediodine, tannic acid and acetic acid or their impregnating equivalents,adapted to transmute ordinary paper into a safety paper having the powerof setting ink and causing discoloration when ink eradicators areapplied to ink written on its surfaces, whereby said safety paper isproduced commercially dry without requiring any further drying.

FRANK S. WOOD.

